1. Field of the Invention
The present invention relates to liquid crystal displays and, more particularly, to a technique suitable for use in a transflective liquid crystal display provided with a backlight and a reflection film.
2. Description of the Related Art
Substantially all mobile phones and mobile information terminals are now provided with liquid crystal displays, and recently, many such mobile electronic apparatuses have been provided with transflective liquid crystal displays.
In general, a transflective liquid crystal display includes a reflector provided on the interior or exterior of a pair of transparent substrates for reflecting incident light from outside and also includes a backlight at the back side thereof. The transflective liquid crystal display can be used as a reflective liquid crystal display and as a transmissive liquid crystal display by switching between a reflective mode in which solar light or an external illumination is used as a light source and a transmissive mode in which light from the backlight is used as a light source.
FIG. 5 is a partial sectional view of a conventional transflective liquid crystal display. In a conventional transflective liquid crystal display 100 shown in the drawing, a first substrate 110 and a second substrate 120, which are composed of a transparent material, such as glass, are opposed to each other, and a liquid crystal layer 130 is enclosed therebetween.
An electrode layer 115 and an alignment film 116 are deposited in that order on a surface of the first substrate 110 facing the liquid crystal layer 130. An electrode layer 125 and an alignment film 126 are deposited in that order on a surface of the second substrate 120 facing the liquid crystal layer 130.
A polarizer 118 is provided on another surface of the first substrate 110 opposite to the liquid crystal layer 130 (i.e., the outer surface of the substrate 110), and a reflector 119 having a reflection film 119a composed of a metal is provided on the outer surface thereof such that the reflection film 119a faces the polarizer 118. A polarizer 128 is provided on the outer surface of the second substrate 120. A backlight 105 for transmissive display is provided on the back of the liquid crystal display 100.
The transflective liquid crystal display 100 having the structure described above is used, for example, as a display area of a mobile phone. When there is sufficient external light, the transflective liquid crystal display 100 operates in the reflective mode in which the backlight 105 is off, and in an environment where there is insufficient external light, it operates in the transmissive mode in which the backlight 105 is on.
However, in the transflective liquid crystal display 100, since the reflector 119 is placed on the exterior of the substrate 110, light entering the liquid crystal display 100 from outside must pass through two substrates, 110 and 120, and two polarizers, 118 and 128, before being reflected by the reflector 119. Therefore, the propagation loss of light is increased, and it is not possible to obtain satisfactory brightness when the transflective liquid crystal display 100 is used as a reflective liquid crystal display.
On the other hand, in the transmissive mode in which the liquid crystal display 100 is used as a transmissive liquid crystal display, although the reflector 119 must transmit light from the backlight 105, the thickness of the reflection film 119a is usually set at 1,000 to 1,500 xc3x85 in order to increase the reflectance of light. That is, pores are made in the reflection film 119a in order to transmit light.
However, in the method in which light from the backlight 105 is transmitted by providing the pores in the reflection film 119a, if the aperture ratio of the pores of the reflection film 119a is increased, the reflectance of the reflection film 119a is decreased, thereby decreasing brightness in the reflective mode. Therefore, it is not possible to sufficiently increase the aperture ratio, and satisfactorily bright display is not obtained when the backlight 105 is lit.
In order to solve the problems described above, a structure is disclosed, in which a reflector is placed between two substrates constituting a liquid crystal display so that the number of layers of substrates and polarizers through which light passes before reaching the reflector is decreased, and, by suppressing the propagation loss of light in the reflective mode, brighter reflective display can be obtained. By using such a structure, since display brightness in the reflective mode is ensured where possible, it is believed that brightness in the transmissive mode can be increased by decreasing the thickness of the reflection film for reflecting light to approximately 300 xc3x85, but brightness in the reflective mode is slightly sacrificed.
However, even if such a structure is used, although the display brightness in the transmissive mode is improved, the brightness in the reflective mode is the same as that of the liquid crystal display 100. If the thickness of the reflection film is increased to a certain degree by giving a high priority to the brightness in the reflective mode, the brightness in the transmissive mode becomes insufficient.
As described above, a transflective liquid crystal display in which satisfactorily bright, easily visible display is performed both in the reflective mode and in the transmissive mode has not yet been produced.
It is an object of the present invention to provide a transflective liquid crystal display in which a bright display is obtained by efficiently reflecting light in the reflective mode, and also in which bright display is obtained by satisfactorily transmitting light in the transmissive mode in which a backlight is lit. It is another object of the present invention to provide a transflector which is suitable for use in such a liquid crystal display.
In one aspect of the present invention, a liquid crystal display includes a pair of substrates which oppose each other with a liquid crystal layer therebetween, and a light source provided on the exterior of one of the substrates. At least an organic film, a metallic reflection film, an overcoat film, an electrode layer, and an alignment film are formed on the inner face of one of the substrates. Many concave portions are contiguously formed on a surface of the organic film, the inner surface of each concave portion constituting a part of a spherical surface, and the metallic reflection film has a thickness of 80 to 500 xc3x85.
In the construction of the present invention described above, since many concave portions are contiguously formed on the surface of the organic film provided with the reflection film for reflecting light entering the liquid crystal display from outside, the inner surface of each concave portion constituting a part of a spherical surface, it is possible to greatly improve the reflection efficiency of light in comparison to the conventional transflective liquid crystal display. Therefore, it is possible to improve the transmittance of the liquid crystal display by decreasing the thickness of the metallic reflection film so that a bright display is also obtained for the transmissive liquid crystal display. Consequently, a bright display can be obtained both in the reflective mode and in the transmissive mode. Moreover, since bright display is enabled in the reflective mode, it is not necessary to turn on the backlight even when the liquid crystal display is used in a slightly dark environment. Consequently, power consumption can be reduced in an electronic apparatus provided with the liquid crystal display of the present invention.
In the liquid crystal display, preferably, the metallic reflection film has a thickness of 80 to 100 xc3x85.
In such a construction, since the transmittance of the liquid crystal display can be improved by decreasing the thickness of the metallic reflection film, it is possible to obtain a liquid crystal display exhibiting superior visibility. Moreover, since the liquid crystal display of the present invention has superior transmittance, it is possible to decrease the amount of light of the backlight required. Consequently, in the liquid crystal display of the present invention, it is possible to reduce the power consumption of the backlight which constitutes the majority of the power consumption of an electronic apparatus provided with the liquid crystal display of the present invention.
In the liquid crystal display, preferably, the depth of the concave portions is in the range of 0.1 to 3 xcexcm, the inclination angle of the inner surface of each concave portion is in the range of xe2x88x9230 degrees to +30 degrees, and the pitch of the adjoining concave portions is in the range of 5 to 50 xcexcm.
In such a construction, since the surface configuration of the organic film is optimized, incident light from outside is more efficiently reflected, and thereby brighter display can be obtained.
In another aspect of the present invention, a transflector includes a reflection layer, the reflection layer including a metallic film deposited on a surface thereof, many concave portions being contiguously formed on the surface, the inner surface of each concave portion constituting a part of a spherical surface. The depth of the concave portions is in the range of 0.1 to 3 xcexcm, the inclination angle of the inner surface of each concave portion is in the range of xe2x88x9230 degrees to +30 degrees, the pitch of the adjoining concave portions is in the range of 5 to 50 xcexcm, and the thickness of the metallic film is 80 to 500 xc3x85.
In such a construction of the present invention, since the surface of the reflection layer can be formed into an optimum shape, light can be reflected more efficiently. By decreasing the thickness of the metallic film placed on the surface of the reflection layer to the value described above, transmittance can be improved. Consequently, in both cases when light is reflected and when light is transmitted, the transflector exhibits superior characteristics.
In another aspect of the present invention, a liquid crystal display includes the transflector described above.
In such a construction, it is possible to obtain a liquid crystal display having superior visibility in which bright display is obtained both in the reflective mode and in the transmissive mode.